Ascaris lumbricoides var. suum is a parasitic intestinal nematode which possesses an anaerobic energy metabolism. Carbohydrates are dissimilated to a mixture of volatile acids and succinate. Studies are continuing on the pathway of formation of the volatile acids, particularly alpha-methybutyrate and alpha-methylvalerate. Ascaris muscle differs biochemically from mammalian muscle in many respects. It functions anaerobically. Pyruvate kinase activity is barely detectable. Lactate is not formed by intact worms. In spite of the anaerobic nature of Ascaris muscle, mitochondria are present. Studies are in progress to better define the relationships between cytoplasmic and mitochondrial metabolisms. Malate, formed in the cytoplasm via CO2 fixation into phosphoenolpyruvate, serves as the mitochondrial substrate. In the mitochondrion, malate dismutates to form succinate and pyruvate with the concomitant anaerobic formation of ATP. A number of anti-cestodal agents have been found to inhibit the P32-ATP exchange reaction in both cestode and Ascaris mitochondria. It is proposed to continue these studies on phosphorylating Ascaris mitochondrial systems in an attempt to better localize the possible mode of action of these drugs. Effects of these agents on net ATP forming systems in both Ascaris and Hymenolepis diminuta are being investigated, as are the roles of transhydrogenases in hydride ion translocation in these anaerobically functioning mitochondria. Studies of the intermediary metabolism of three filarial worms, Litomosoides carinii, Dipetalonema witei (viteae) and Brugia pahangi are continuing.